-
lr_parser
-
lr_parser(): void
-
lr_parser(Scanner): void
-
_error_sync_size: int
-
error_sync_size(): int
-
production_table(): short[][]
-
action_table(): short[][]
-
reduce_table(): short[][]
-
start_state(): int
-
start_production(): int
-
EOF_sym(): int
-
error_sym(): int
-
_done_parsing: boolean
-
done_parsing(): void
-
tos: int
-
cur_token: Symbol
-
stack: Stack
-
production_tab: short[][]
-
action_tab: short[][]
-
reduce_tab: short[][]
-
_scanner: Scanner
-
setScanner(Scanner): void
-
getScanner(): Scanner
-
do_action(int, lr_parser, Stack, int): Symbol
-
user_init(): void
-
init_actions(): void
-
scan(): Symbol
-
report_fatal_error(String, Object): void
-
report_error(String, Object): void
-
syntax_error(Symbol): void
-
unrecovered_syntax_error(Symbol): void
-
get_action(int, int): short
-
get_reduce(int, int): short
-
parse(): Symbol
-
debug_message(String): void
-
dump_stack(): void
-
debug_reduce(int, int, int): void
-
debug_shift(Symbol): void
-
debug_stack(): void
-
debug_parse(): Symbol
-
error_recovery(boolean): boolean
-
shift_under_error(): boolean
-
find_recovery_config(boolean): boolean
-
lookahead: Symbol[]
-
lookahead_pos: int
-
read_lookahead(): void
-
cur_err_token(): Symbol
-
advance_lookahead(): boolean
-
restart_lookahead(): void
-
try_parse_ahead(boolean): boolean
-
parse_lookahead(boolean): void
-
unpackFromStrings(String[]): short[][]
-
/*
* Copyright (c) 2003, 2005, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
package com.sun.java_cup.internal.runtime;
import java.util.Stack;
This class implements a skeleton table driven LR parser. In general,
LR parsers are a form of bottom up shift-reduce parsers. Shift-reduce
parsers act by shifting input onto a parse stack until the Symbols
matching the right hand side of a production appear on the top of the
stack. Once this occurs, a reduce is performed. This involves removing
the Symbols corresponding to the right hand side of the production
(the so called "handle") and replacing them with the non-terminal from
the left hand side of the production.
To control the decision of whether to shift or reduce at any given point,
the parser uses a state machine (the "viable prefix recognition machine"
built by the parser generator). The current state of the machine is placed
on top of the parse stack (stored as part of a Symbol object representing
a terminal or non terminal). The parse action table is consulted
(using the current state and the current lookahead Symbol as indexes) to
determine whether to shift or to reduce. When the parser shifts, it
changes to a new state by pushing a new Symbol (containing a new state)
onto the stack. When the parser reduces, it pops the handle (right hand
side of a production) off the stack. This leaves the parser in the state
it was in before any of those Symbols were matched. Next the reduce-goto
table is consulted (using the new state and current lookahead Symbol as
indexes) to determine a new state to go to. The parser then shifts to
this goto state by pushing the left hand side Symbol of the production
(also containing the new state) onto the stack.
This class actually provides four LR parsers. The methods parse() and
debug_parse() provide two versions of the main parser (the only difference
being that debug_parse() emits debugging trace messages as it parses).
In addition to these main parsers, the error recovery mechanism uses two
more. One of these is used to simulate "parsing ahead" in the input
without carrying out actions (to verify that a potential error recovery
has worked), and the other is used to parse through buffered "parse ahead"
input in order to execute all actions and re-synchronize the actual parser
configuration.
This is an abstract class which is normally filled out by a subclass
generated by the JavaCup parser generator. In addition to supplying
the actual parse tables, generated code also supplies methods which
invoke various pieces of user supplied code, provide access to certain
special Symbols (e.g., EOF and error), etc. Specifically, the following
abstract methods are normally supplied by generated code:
- short[][] production_table()
- Provides a reference to the production table (indicating the index of
the left hand side non terminal and the length of the right hand side
for each production in the grammar).
- short[][] action_table()
- Provides a reference to the parse action table.
- short[][] reduce_table()
- Provides a reference to the reduce-goto table.
- int start_state()
- Indicates the index of the start state.
- int start_production()
- Indicates the index of the starting production.
- int EOF_sym()
- Indicates the index of the EOF Symbol.
- int error_sym()
- Indicates the index of the error Symbol.
- Symbol do_action()
- Executes a piece of user supplied action code. This always comes at
the point of a reduce in the parse, so this code also allocates and
fills in the left hand side non terminal Symbol object that is to be
pushed onto the stack for the reduce.
- void init_actions()
- Code to initialize a special object that encapsulates user supplied
actions (this object is used by do_action() to actually carry out the
actions).
In addition to these routines that must be supplied by the
generated subclass there are also a series of routines that may
be supplied. These include:
- Symbol scan()
- Used to get the next input Symbol from the scanner.
- Scanner getScanner()
- Used to provide a scanner for the default implementation of
scan().
- int error_sync_size()
- This determines how many Symbols past the point of an error
must be parsed without error in order to consider a recovery to
be valid. This defaults to 3. Values less than 2 are not
recommended.
- void report_error(String message, Object info)
- This method is called to report an error. The default implementation
simply prints a message to System.err and where the error occurred.
This method is often replaced in order to provide a more sophisticated
error reporting mechanism.
- void report_fatal_error(String message, Object info)
- This method is called when a fatal error that cannot be recovered from
is encountered. In the default implementation, it calls
report_error() to emit a message, then throws an exception.
- void syntax_error(Symbol cur_token)
- This method is called as soon as syntax error is detected (but
before recovery is attempted). In the default implementation it
invokes: report_error("Syntax error", null);
- void unrecovered_syntax_error(Symbol cur_token)
- This method is called if syntax error recovery fails. In the default
implementation it invokes:
report_fatal_error("Couldn't repair and continue parse", null);
Author: Frank Flannery See Also:
/** This class implements a skeleton table driven LR parser. In general,
* LR parsers are a form of bottom up shift-reduce parsers. Shift-reduce
* parsers act by shifting input onto a parse stack until the Symbols
* matching the right hand side of a production appear on the top of the
* stack. Once this occurs, a reduce is performed. This involves removing
* the Symbols corresponding to the right hand side of the production
* (the so called "handle") and replacing them with the non-terminal from
* the left hand side of the production. <p>
*
* To control the decision of whether to shift or reduce at any given point,
* the parser uses a state machine (the "viable prefix recognition machine"
* built by the parser generator). The current state of the machine is placed
* on top of the parse stack (stored as part of a Symbol object representing
* a terminal or non terminal). The parse action table is consulted
* (using the current state and the current lookahead Symbol as indexes) to
* determine whether to shift or to reduce. When the parser shifts, it
* changes to a new state by pushing a new Symbol (containing a new state)
* onto the stack. When the parser reduces, it pops the handle (right hand
* side of a production) off the stack. This leaves the parser in the state
* it was in before any of those Symbols were matched. Next the reduce-goto
* table is consulted (using the new state and current lookahead Symbol as
* indexes) to determine a new state to go to. The parser then shifts to
* this goto state by pushing the left hand side Symbol of the production
* (also containing the new state) onto the stack.<p>
*
* This class actually provides four LR parsers. The methods parse() and
* debug_parse() provide two versions of the main parser (the only difference
* being that debug_parse() emits debugging trace messages as it parses).
* In addition to these main parsers, the error recovery mechanism uses two
* more. One of these is used to simulate "parsing ahead" in the input
* without carrying out actions (to verify that a potential error recovery
* has worked), and the other is used to parse through buffered "parse ahead"
* input in order to execute all actions and re-synchronize the actual parser
* configuration.<p>
*
* This is an abstract class which is normally filled out by a subclass
* generated by the JavaCup parser generator. In addition to supplying
* the actual parse tables, generated code also supplies methods which
* invoke various pieces of user supplied code, provide access to certain
* special Symbols (e.g., EOF and error), etc. Specifically, the following
* abstract methods are normally supplied by generated code:
* <dl compact>
* <dt> short[][] production_table()
* <dd> Provides a reference to the production table (indicating the index of
* the left hand side non terminal and the length of the right hand side
* for each production in the grammar).
* <dt> short[][] action_table()
* <dd> Provides a reference to the parse action table.
* <dt> short[][] reduce_table()
* <dd> Provides a reference to the reduce-goto table.
* <dt> int start_state()
* <dd> Indicates the index of the start state.
* <dt> int start_production()
* <dd> Indicates the index of the starting production.
* <dt> int EOF_sym()
* <dd> Indicates the index of the EOF Symbol.
* <dt> int error_sym()
* <dd> Indicates the index of the error Symbol.
* <dt> Symbol do_action()
* <dd> Executes a piece of user supplied action code. This always comes at
* the point of a reduce in the parse, so this code also allocates and
* fills in the left hand side non terminal Symbol object that is to be
* pushed onto the stack for the reduce.
* <dt> void init_actions()
* <dd> Code to initialize a special object that encapsulates user supplied
* actions (this object is used by do_action() to actually carry out the
* actions).
* </dl>
*
* In addition to these routines that <i>must</i> be supplied by the
* generated subclass there are also a series of routines that <i>may</i>
* be supplied. These include:
* <dl>
* <dt> Symbol scan()
* <dd> Used to get the next input Symbol from the scanner.
* <dt> Scanner getScanner()
* <dd> Used to provide a scanner for the default implementation of
* scan().
* <dt> int error_sync_size()
* <dd> This determines how many Symbols past the point of an error
* must be parsed without error in order to consider a recovery to
* be valid. This defaults to 3. Values less than 2 are not
* recommended.
* <dt> void report_error(String message, Object info)
* <dd> This method is called to report an error. The default implementation
* simply prints a message to System.err and where the error occurred.
* This method is often replaced in order to provide a more sophisticated
* error reporting mechanism.
* <dt> void report_fatal_error(String message, Object info)
* <dd> This method is called when a fatal error that cannot be recovered from
* is encountered. In the default implementation, it calls
* report_error() to emit a message, then throws an exception.
* <dt> void syntax_error(Symbol cur_token)
* <dd> This method is called as soon as syntax error is detected (but
* before recovery is attempted). In the default implementation it
* invokes: report_error("Syntax error", null);
* <dt> void unrecovered_syntax_error(Symbol cur_token)
* <dd> This method is called if syntax error recovery fails. In the default
* implementation it invokes:<br>
* report_fatal_error("Couldn't repair and continue parse", null);
* </dl>
*
* @see com.sun.java_cup.internal.runtime.Symbol
* @see com.sun.java_cup.internal.runtime.Symbol
* @see com.sun.java_cup.internal.runtime.virtual_parse_stack
* @author Frank Flannery
*/
public abstract class lr_parser {
/*-----------------------------------------------------------*/
/*--- Constructor(s) ----------------------------------------*/
/*-----------------------------------------------------------*/
Simple constructor. /** Simple constructor. */
public lr_parser()
{
/* nothing to do here */
}
Constructor that sets the default scanner. [CSA/davidm] /** Constructor that sets the default scanner. [CSA/davidm] */
public lr_parser(Scanner s) {
this(); /* in case default constructor someday does something */
setScanner(s);
}
/*-----------------------------------------------------------*/
/*--- (Access to) Static (Class) Variables ------------------*/
/*-----------------------------------------------------------*/
The default number of Symbols after an error we much match to consider
it recovered from.
/** The default number of Symbols after an error we much match to consider
* it recovered from.
*/
protected final static int _error_sync_size = 3;
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
The number of Symbols after an error we much match to consider it
recovered from.
/** The number of Symbols after an error we much match to consider it
* recovered from.
*/
protected int error_sync_size() {return _error_sync_size; }
/*-----------------------------------------------------------*/
/*--- (Access to) Instance Variables ------------------------*/
/*-----------------------------------------------------------*/
Table of production information (supplied by generated subclass).
This table contains one entry per production and is indexed by
the negative-encoded values (reduce actions) in the action_table.
Each entry has two parts, the index of the non-terminal on the
left hand side of the production, and the number of Symbols
on the right hand side.
/** Table of production information (supplied by generated subclass).
* This table contains one entry per production and is indexed by
* the negative-encoded values (reduce actions) in the action_table.
* Each entry has two parts, the index of the non-terminal on the
* left hand side of the production, and the number of Symbols
* on the right hand side.
*/
public abstract short[][] production_table();
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
The action table (supplied by generated subclass). This table is
indexed by state and terminal number indicating what action is to
be taken when the parser is in the given state (i.e., the given state
is on top of the stack) and the given terminal is next on the input.
States are indexed using the first dimension, however, the entries for
a given state are compacted and stored in adjacent index, value pairs
which are searched for rather than accessed directly (see get_action()).
The actions stored in the table will be either shifts, reduces, or
errors. Shifts are encoded as positive values (one greater than the
state shifted to). Reduces are encoded as negative values (one less
than the production reduced by). Error entries are denoted by zero.
See Also: - get_action.get_action
/** The action table (supplied by generated subclass). This table is
* indexed by state and terminal number indicating what action is to
* be taken when the parser is in the given state (i.e., the given state
* is on top of the stack) and the given terminal is next on the input.
* States are indexed using the first dimension, however, the entries for
* a given state are compacted and stored in adjacent index, value pairs
* which are searched for rather than accessed directly (see get_action()).
* The actions stored in the table will be either shifts, reduces, or
* errors. Shifts are encoded as positive values (one greater than the
* state shifted to). Reduces are encoded as negative values (one less
* than the production reduced by). Error entries are denoted by zero.
*
* @see com.sun.java_cup.internal.runtime.lr_parser#get_action
*/
public abstract short[][] action_table();
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
The reduce-goto table (supplied by generated subclass). This
table is indexed by state and non-terminal number and contains
state numbers. States are indexed using the first dimension, however,
the entries for a given state are compacted and stored in adjacent
index, value pairs which are searched for rather than accessed
directly (see get_reduce()). When a reduce occurs, the handle
(corresponding to the RHS of the matched production) is popped off
the stack. The new top of stack indicates a state. This table is
then indexed by that state and the LHS of the reducing production to
indicate where to "shift" to.
See Also: - get_reduce.get_reduce
/** The reduce-goto table (supplied by generated subclass). This
* table is indexed by state and non-terminal number and contains
* state numbers. States are indexed using the first dimension, however,
* the entries for a given state are compacted and stored in adjacent
* index, value pairs which are searched for rather than accessed
* directly (see get_reduce()). When a reduce occurs, the handle
* (corresponding to the RHS of the matched production) is popped off
* the stack. The new top of stack indicates a state. This table is
* then indexed by that state and the LHS of the reducing production to
* indicate where to "shift" to.
*
* @see com.sun.java_cup.internal.runtime.lr_parser#get_reduce
*/
public abstract short[][] reduce_table();
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
The index of the start state (supplied by generated subclass). /** The index of the start state (supplied by generated subclass). */
public abstract int start_state();
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
The index of the start production (supplied by generated subclass). /** The index of the start production (supplied by generated subclass). */
public abstract int start_production();
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
The index of the end of file terminal Symbol (supplied by generated
subclass).
/** The index of the end of file terminal Symbol (supplied by generated
* subclass).
*/
public abstract int EOF_sym();
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
The index of the special error Symbol (supplied by generated subclass). /** The index of the special error Symbol (supplied by generated subclass). */
public abstract int error_sym();
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
Internal flag to indicate when parser should quit. /** Internal flag to indicate when parser should quit. */
protected boolean _done_parsing = false;
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
This method is called to indicate that the parser should quit. This is
normally called by an accept action, but can be used to cancel parsing
early in other circumstances if desired.
/** This method is called to indicate that the parser should quit. This is
* normally called by an accept action, but can be used to cancel parsing
* early in other circumstances if desired.
*/
public void done_parsing()
{
_done_parsing = true;
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/* Global parse state shared by parse(), error recovery, and
* debugging routines */
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
Indication of the index for top of stack (for use by actions). /** Indication of the index for top of stack (for use by actions). */
protected int tos;
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
The current lookahead Symbol. /** The current lookahead Symbol. */
protected Symbol cur_token;
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
The parse stack itself. /** The parse stack itself. */
protected Stack stack = new Stack();
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
Direct reference to the production table. /** Direct reference to the production table. */
protected short[][] production_tab;
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
Direct reference to the action table. /** Direct reference to the action table. */
protected short[][] action_tab;
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
Direct reference to the reduce-goto table. /** Direct reference to the reduce-goto table. */
protected short[][] reduce_tab;
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
This is the scanner object used by the default implementation
of scan() to get Symbols. To avoid name conflicts with existing
code, this field is private. [CSA/davidm] /** This is the scanner object used by the default implementation
* of scan() to get Symbols. To avoid name conflicts with existing
* code, this field is private. [CSA/davidm] */
private Scanner _scanner;
Simple accessor method to set the default scanner.
/**
* Simple accessor method to set the default scanner.
*/
public void setScanner(Scanner s) { _scanner = s; }
Simple accessor method to get the default scanner.
/**
* Simple accessor method to get the default scanner.
*/
public Scanner getScanner() { return _scanner; }
/*-----------------------------------------------------------*/
/*--- General Methods ---------------------------------------*/
/*-----------------------------------------------------------*/
Perform a bit of user supplied action code (supplied by generated
subclass). Actions are indexed by an internal action number assigned
at parser generation time.
Params: - act_num – the internal index of the action to be performed.
- parser – the parser object we are acting for.
- stack – the parse stack of that object.
- top – the index of the top element of the parse stack.
/** Perform a bit of user supplied action code (supplied by generated
* subclass). Actions are indexed by an internal action number assigned
* at parser generation time.
*
* @param act_num the internal index of the action to be performed.
* @param parser the parser object we are acting for.
* @param stack the parse stack of that object.
* @param top the index of the top element of the parse stack.
*/
public abstract Symbol do_action(
int act_num,
lr_parser parser,
Stack stack,
int top)
throws java.lang.Exception;
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
User code for initialization inside the parser. Typically this
initializes the scanner. This is called before the parser requests
the first Symbol. Here this is just a placeholder for subclasses that
might need this and we perform no action. This method is normally
overridden by the generated code using this contents of the "init with"
clause as its body.
/** User code for initialization inside the parser. Typically this
* initializes the scanner. This is called before the parser requests
* the first Symbol. Here this is just a placeholder for subclasses that
* might need this and we perform no action. This method is normally
* overridden by the generated code using this contents of the "init with"
* clause as its body.
*/
public void user_init() throws java.lang.Exception { }
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
Initialize the action object. This is called before the parser does
any parse actions. This is filled in by generated code to create
an object that encapsulates all action code.
/** Initialize the action object. This is called before the parser does
* any parse actions. This is filled in by generated code to create
* an object that encapsulates all action code.
*/
protected abstract void init_actions() throws java.lang.Exception;
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
Get the next Symbol from the input (supplied by generated subclass).
Once end of file has been reached, all subsequent calls to scan
should return an EOF Symbol (which is Symbol number 0). By default
this method returns getScanner().next_token(); this implementation
can be overriden by the generated parser using the code declared in
the "scan with" clause. Do not recycle objects; every call to
scan() should return a fresh object.
/** Get the next Symbol from the input (supplied by generated subclass).
* Once end of file has been reached, all subsequent calls to scan
* should return an EOF Symbol (which is Symbol number 0). By default
* this method returns getScanner().next_token(); this implementation
* can be overriden by the generated parser using the code declared in
* the "scan with" clause. Do not recycle objects; every call to
* scan() should return a fresh object.
*/
public Symbol scan() throws java.lang.Exception {
return getScanner().next_token();
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
Report a fatal error. This method takes a message string and an
additional object (to be used by specializations implemented in
subclasses). Here in the base class a very simple implementation
is provided which reports the error then throws an exception.
Params: - message – an error message.
- info – an extra object reserved for use by specialized subclasses.
/** Report a fatal error. This method takes a message string and an
* additional object (to be used by specializations implemented in
* subclasses). Here in the base class a very simple implementation
* is provided which reports the error then throws an exception.
*
* @param message an error message.
* @param info an extra object reserved for use by specialized subclasses.
*/
public void report_fatal_error(
String message,
Object info)
throws java.lang.Exception
{
/* stop parsing (not really necessary since we throw an exception, but) */
done_parsing();
/* use the normal error message reporting to put out the message */
report_error(message, info);
/* throw an exception */
throw new Exception("Can't recover from previous error(s)");
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
Report a non fatal error (or warning). This method takes a message
string and an additional object (to be used by specializations
implemented in subclasses). Here in the base class a very simple
implementation is provided which simply prints the message to
System.err.
Params: - message – an error message.
- info – an extra object reserved for use by specialized subclasses.
/** Report a non fatal error (or warning). This method takes a message
* string and an additional object (to be used by specializations
* implemented in subclasses). Here in the base class a very simple
* implementation is provided which simply prints the message to
* System.err.
*
* @param message an error message.
* @param info an extra object reserved for use by specialized subclasses.
*/
public void report_error(String message, Object info)
{
System.err.print(message);
if (info instanceof Symbol)
if (((Symbol)info).left != -1)
System.err.println(" at character " + ((Symbol)info).left +
" of input");
else System.err.println("");
else System.err.println("");
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
This method is called when a syntax error has been detected and recovery
is about to be invoked. Here in the base class we just emit a
"Syntax error" error message.
Params: - cur_token – the current lookahead Symbol.
/** This method is called when a syntax error has been detected and recovery
* is about to be invoked. Here in the base class we just emit a
* "Syntax error" error message.
*
* @param cur_token the current lookahead Symbol.
*/
public void syntax_error(Symbol cur_token)
{
report_error("Syntax error", cur_token);
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
This method is called if it is determined that syntax error recovery
has been unsuccessful. Here in the base class we report a fatal error.
Params: - cur_token – the current lookahead Symbol.
/** This method is called if it is determined that syntax error recovery
* has been unsuccessful. Here in the base class we report a fatal error.
*
* @param cur_token the current lookahead Symbol.
*/
public void unrecovered_syntax_error(Symbol cur_token)
throws java.lang.Exception
{
report_fatal_error("Couldn't repair and continue parse", cur_token);
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
Fetch an action from the action table. The table is broken up into
rows, one per state (rows are indexed directly by state number).
Within each row, a list of index, value pairs are given (as sequential
entries in the table), and the list is terminated by a default entry
(denoted with a Symbol index of -1). To find the proper entry in a row
we do a linear or binary search (depending on the size of the row).
Params: - state – the state index of the action being accessed.
- sym – the Symbol index of the action being accessed.
/** Fetch an action from the action table. The table is broken up into
* rows, one per state (rows are indexed directly by state number).
* Within each row, a list of index, value pairs are given (as sequential
* entries in the table), and the list is terminated by a default entry
* (denoted with a Symbol index of -1). To find the proper entry in a row
* we do a linear or binary search (depending on the size of the row).
*
* @param state the state index of the action being accessed.
* @param sym the Symbol index of the action being accessed.
*/
protected final short get_action(int state, int sym)
{
short tag;
int first, last, probe;
short[] row = action_tab[state];
/* linear search if we are < 10 entries */
if (row.length < 20)
for (probe = 0; probe < row.length; probe++)
{
/* is this entry labeled with our Symbol or the default? */
tag = row[probe++];
if (tag == sym || tag == -1)
{
/* return the next entry */
return row[probe];
}
}
/* otherwise binary search */
else
{
first = 0;
last = (row.length-1)/2 - 1; /* leave out trailing default entry */
while (first <= last)
{
probe = (first+last)/2;
if (sym == row[probe*2])
return row[probe*2+1];
else if (sym > row[probe*2])
first = probe+1;
else
last = probe-1;
}
/* not found, use the default at the end */
return row[row.length-1];
}
/* shouldn't happened, but if we run off the end we return the
default (error == 0) */
return 0;
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
Fetch a state from the reduce-goto table. The table is broken up into
rows, one per state (rows are indexed directly by state number).
Within each row, a list of index, value pairs are given (as sequential
entries in the table), and the list is terminated by a default entry
(denoted with a Symbol index of -1). To find the proper entry in a row
we do a linear search.
Params: - state – the state index of the entry being accessed.
- sym – the Symbol index of the entry being accessed.
/** Fetch a state from the reduce-goto table. The table is broken up into
* rows, one per state (rows are indexed directly by state number).
* Within each row, a list of index, value pairs are given (as sequential
* entries in the table), and the list is terminated by a default entry
* (denoted with a Symbol index of -1). To find the proper entry in a row
* we do a linear search.
*
* @param state the state index of the entry being accessed.
* @param sym the Symbol index of the entry being accessed.
*/
protected final short get_reduce(int state, int sym)
{
short tag;
short[] row = reduce_tab[state];
/* if we have a null row we go with the default */
if (row == null)
return -1;
for (int probe = 0; probe < row.length; probe++)
{
/* is this entry labeled with our Symbol or the default? */
tag = row[probe++];
if (tag == sym || tag == -1)
{
/* return the next entry */
return row[probe];
}
}
/* if we run off the end we return the default (error == -1) */
return -1;
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
This method provides the main parsing routine. It returns only when
done_parsing() has been called (typically because the parser has
accepted, or a fatal error has been reported). See the header
documentation for the class regarding how shift/reduce parsers operate
and how the various tables are used.
/** This method provides the main parsing routine. It returns only when
* done_parsing() has been called (typically because the parser has
* accepted, or a fatal error has been reported). See the header
* documentation for the class regarding how shift/reduce parsers operate
* and how the various tables are used.
*/
public Symbol parse() throws java.lang.Exception
{
/* the current action code */
int act;
/* the Symbol/stack element returned by a reduce */
Symbol lhs_sym = null;
/* information about production being reduced with */
short handle_size, lhs_sym_num;
/* set up direct reference to tables to drive the parser */
production_tab = production_table();
action_tab = action_table();
reduce_tab = reduce_table();
/* initialize the action encapsulation object */
init_actions();
/* do user initialization */
user_init();
/* get the first token */
cur_token = scan();
/* push dummy Symbol with start state to get us underway */
stack.removeAllElements();
stack.push(new Symbol(0, start_state()));
tos = 0;
/* continue until we are told to stop */
for (_done_parsing = false; !_done_parsing; )
{
/* Check current token for freshness. */
if (cur_token.used_by_parser)
throw new Error("Symbol recycling detected (fix your scanner).");
/* current state is always on the top of the stack */
/* look up action out of the current state with the current input */
act = get_action(((Symbol)stack.peek()).parse_state, cur_token.sym);
/* decode the action -- > 0 encodes shift */
if (act > 0)
{
/* shift to the encoded state by pushing it on the stack */
cur_token.parse_state = act-1;
cur_token.used_by_parser = true;
stack.push(cur_token);
tos++;
/* advance to the next Symbol */
cur_token = scan();
}
/* if its less than zero, then it encodes a reduce action */
else if (act < 0)
{
/* perform the action for the reduce */
lhs_sym = do_action((-act)-1, this, stack, tos);
/* look up information about the production */
lhs_sym_num = production_tab[(-act)-1][0];
handle_size = production_tab[(-act)-1][1];
/* pop the handle off the stack */
for (int i = 0; i < handle_size; i++)
{
stack.pop();
tos--;
}
/* look up the state to go to from the one popped back to */
act = get_reduce(((Symbol)stack.peek()).parse_state, lhs_sym_num);
/* shift to that state */
lhs_sym.parse_state = act;
lhs_sym.used_by_parser = true;
stack.push(lhs_sym);
tos++;
}
/* finally if the entry is zero, we have an error */
else if (act == 0)
{
/* call user syntax error reporting routine */
syntax_error(cur_token);
/* try to error recover */
if (!error_recovery(false))
{
/* if that fails give up with a fatal syntax error */
unrecovered_syntax_error(cur_token);
/* just in case that wasn't fatal enough, end parse */
done_parsing();
} else {
lhs_sym = (Symbol)stack.peek();
}
}
}
return lhs_sym;
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
Write a debugging message to System.err for the debugging version
of the parser.
Params: - mess – the text of the debugging message.
/** Write a debugging message to System.err for the debugging version
* of the parser.
*
* @param mess the text of the debugging message.
*/
public void debug_message(String mess)
{
System.err.println(mess);
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
Dump the parse stack for debugging purposes. /** Dump the parse stack for debugging purposes. */
public void dump_stack()
{
if (stack == null)
{
debug_message("# Stack dump requested, but stack is null");
return;
}
debug_message("============ Parse Stack Dump ============");
/* dump the stack */
for (int i=0; i<stack.size(); i++)
{
debug_message("Symbol: " + ((Symbol)stack.elementAt(i)).sym +
" State: " + ((Symbol)stack.elementAt(i)).parse_state);
}
debug_message("==========================================");
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
Do debug output for a reduce.
Params: - prod_num – the production we are reducing with.
- nt_num – the index of the LHS non terminal.
- rhs_size – the size of the RHS.
/** Do debug output for a reduce.
*
* @param prod_num the production we are reducing with.
* @param nt_num the index of the LHS non terminal.
* @param rhs_size the size of the RHS.
*/
public void debug_reduce(int prod_num, int nt_num, int rhs_size)
{
debug_message("# Reduce with prod #" + prod_num + " [NT=" + nt_num +
", " + "SZ=" + rhs_size + "]");
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
Do debug output for shift.
Params: - shift_tkn – the Symbol being shifted onto the stack.
/** Do debug output for shift.
*
* @param shift_tkn the Symbol being shifted onto the stack.
*/
public void debug_shift(Symbol shift_tkn)
{
debug_message("# Shift under term #" + shift_tkn.sym +
" to state #" + shift_tkn.parse_state);
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
Do debug output for stack state. [CSA]
/** Do debug output for stack state. [CSA]
*/
public void debug_stack() {
StringBuffer sb=new StringBuffer("## STACK:");
for (int i=0; i<stack.size(); i++) {
Symbol s = (Symbol) stack.elementAt(i);
sb.append(" <state "+s.parse_state+", sym "+s.sym+">");
if ((i%3)==2 || (i==(stack.size()-1))) {
debug_message(sb.toString());
sb = new StringBuffer(" ");
}
}
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
Perform a parse with debugging output. This does exactly the
same things as parse(), except that it calls debug_shift() and
debug_reduce() when shift and reduce moves are taken by the parser
and produces various other debugging messages.
/** Perform a parse with debugging output. This does exactly the
* same things as parse(), except that it calls debug_shift() and
* debug_reduce() when shift and reduce moves are taken by the parser
* and produces various other debugging messages.
*/
public Symbol debug_parse()
throws java.lang.Exception
{
/* the current action code */
int act;
/* the Symbol/stack element returned by a reduce */
Symbol lhs_sym = null;
/* information about production being reduced with */
short handle_size, lhs_sym_num;
/* set up direct reference to tables to drive the parser */
production_tab = production_table();
action_tab = action_table();
reduce_tab = reduce_table();
debug_message("# Initializing parser");
/* initialize the action encapsulation object */
init_actions();
/* do user initialization */
user_init();
/* the current Symbol */
cur_token = scan();
debug_message("# Current Symbol is #" + cur_token.sym);
/* push dummy Symbol with start state to get us underway */
stack.removeAllElements();
stack.push(new Symbol(0, start_state()));
tos = 0;
/* continue until we are told to stop */
for (_done_parsing = false; !_done_parsing; )
{
/* Check current token for freshness. */
if (cur_token.used_by_parser)
throw new Error("Symbol recycling detected (fix your scanner).");
/* current state is always on the top of the stack */
//debug_stack();
/* look up action out of the current state with the current input */
act = get_action(((Symbol)stack.peek()).parse_state, cur_token.sym);
/* decode the action -- > 0 encodes shift */
if (act > 0)
{
/* shift to the encoded state by pushing it on the stack */
cur_token.parse_state = act-1;
cur_token.used_by_parser = true;
debug_shift(cur_token);
stack.push(cur_token);
tos++;
/* advance to the next Symbol */
cur_token = scan();
debug_message("# Current token is " + cur_token);
}
/* if its less than zero, then it encodes a reduce action */
else if (act < 0)
{
/* perform the action for the reduce */
lhs_sym = do_action((-act)-1, this, stack, tos);
/* look up information about the production */
lhs_sym_num = production_tab[(-act)-1][0];
handle_size = production_tab[(-act)-1][1];
debug_reduce((-act)-1, lhs_sym_num, handle_size);
/* pop the handle off the stack */
for (int i = 0; i < handle_size; i++)
{
stack.pop();
tos--;
}
/* look up the state to go to from the one popped back to */
act = get_reduce(((Symbol)stack.peek()).parse_state, lhs_sym_num);
debug_message("# Reduce rule: top state " +
((Symbol)stack.peek()).parse_state +
", lhs sym " + lhs_sym_num + " -> state " + act);
/* shift to that state */
lhs_sym.parse_state = act;
lhs_sym.used_by_parser = true;
stack.push(lhs_sym);
tos++;
debug_message("# Goto state #" + act);
}
/* finally if the entry is zero, we have an error */
else if (act == 0)
{
/* call user syntax error reporting routine */
syntax_error(cur_token);
/* try to error recover */
if (!error_recovery(true))
{
/* if that fails give up with a fatal syntax error */
unrecovered_syntax_error(cur_token);
/* just in case that wasn't fatal enough, end parse */
done_parsing();
} else {
lhs_sym = (Symbol)stack.peek();
}
}
}
return lhs_sym;
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/* Error recovery code */
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
Attempt to recover from a syntax error. This returns false if recovery
fails, true if it succeeds. Recovery happens in 4 steps. First we
pop the parse stack down to a point at which we have a shift out
of the top-most state on the error Symbol. This represents the
initial error recovery configuration. If no such configuration is
found, then we fail. Next a small number of "lookahead" or "parse
ahead" Symbols are read into a buffer. The size of this buffer is
determined by error_sync_size() and determines how many Symbols beyond
the error must be matched to consider the recovery a success. Next,
we begin to discard Symbols in attempt to get past the point of error
to a point where we can continue parsing. After each Symbol, we attempt
to "parse ahead" though the buffered lookahead Symbols. The "parse ahead"
process simulates that actual parse, but does not modify the real
parser's configuration, nor execute any actions. If we can parse all
the stored Symbols without error, then the recovery is considered a
success. Once a successful recovery point is determined, we do an
actual parse over the stored input -- modifying the real parse
configuration and executing all actions. Finally, we return the the
normal parser to continue with the overall parse.
Params: - debug – should we produce debugging messages as we parse.
/** Attempt to recover from a syntax error. This returns false if recovery
* fails, true if it succeeds. Recovery happens in 4 steps. First we
* pop the parse stack down to a point at which we have a shift out
* of the top-most state on the error Symbol. This represents the
* initial error recovery configuration. If no such configuration is
* found, then we fail. Next a small number of "lookahead" or "parse
* ahead" Symbols are read into a buffer. The size of this buffer is
* determined by error_sync_size() and determines how many Symbols beyond
* the error must be matched to consider the recovery a success. Next,
* we begin to discard Symbols in attempt to get past the point of error
* to a point where we can continue parsing. After each Symbol, we attempt
* to "parse ahead" though the buffered lookahead Symbols. The "parse ahead"
* process simulates that actual parse, but does not modify the real
* parser's configuration, nor execute any actions. If we can parse all
* the stored Symbols without error, then the recovery is considered a
* success. Once a successful recovery point is determined, we do an
* actual parse over the stored input -- modifying the real parse
* configuration and executing all actions. Finally, we return the the
* normal parser to continue with the overall parse.
*
* @param debug should we produce debugging messages as we parse.
*/
protected boolean error_recovery(boolean debug)
throws java.lang.Exception
{
if (debug) debug_message("# Attempting error recovery");
/* first pop the stack back into a state that can shift on error and
do that shift (if that fails, we fail) */
if (!find_recovery_config(debug))
{
if (debug) debug_message("# Error recovery fails");
return false;
}
/* read ahead to create lookahead we can parse multiple times */
read_lookahead();
/* repeatedly try to parse forward until we make it the required dist */
for (;;)
{
/* try to parse forward, if it makes it, bail out of loop */
if (debug) debug_message("# Trying to parse ahead");
if (try_parse_ahead(debug))
{
break;
}
/* if we are now at EOF, we have failed */
if (lookahead[0].sym == EOF_sym())
{
if (debug) debug_message("# Error recovery fails at EOF");
return false;
}
/* otherwise, we consume another Symbol and try again */
if (debug)
debug_message("# Consuming Symbol #" + cur_err_token().sym);
restart_lookahead();
}
/* we have consumed to a point where we can parse forward */
if (debug) debug_message("# Parse-ahead ok, going back to normal parse");
/* do the real parse (including actions) across the lookahead */
parse_lookahead(debug);
/* we have success */
return true;
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
Determine if we can shift under the special error Symbol out of the
state currently on the top of the (real) parse stack.
/** Determine if we can shift under the special error Symbol out of the
* state currently on the top of the (real) parse stack.
*/
protected boolean shift_under_error()
{
/* is there a shift under error Symbol */
return get_action(((Symbol)stack.peek()).parse_state, error_sym()) > 0;
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
Put the (real) parse stack into error recovery configuration by
popping the stack down to a state that can shift on the special
error Symbol, then doing the shift. If no suitable state exists on
the stack we return false
Params: - debug – should we produce debugging messages as we parse.
/** Put the (real) parse stack into error recovery configuration by
* popping the stack down to a state that can shift on the special
* error Symbol, then doing the shift. If no suitable state exists on
* the stack we return false
*
* @param debug should we produce debugging messages as we parse.
*/
protected boolean find_recovery_config(boolean debug)
{
Symbol error_token;
int act;
if (debug) debug_message("# Finding recovery state on stack");
/* Remember the right-position of the top symbol on the stack */
int right_pos = ((Symbol)stack.peek()).right;
int left_pos = ((Symbol)stack.peek()).left;
/* pop down until we can shift under error Symbol */
while (!shift_under_error())
{
/* pop the stack */
if (debug)
debug_message("# Pop stack by one, state was # " +
((Symbol)stack.peek()).parse_state);
left_pos = ((Symbol)stack.pop()).left;
tos--;
/* if we have hit bottom, we fail */
if (stack.empty())
{
if (debug) debug_message("# No recovery state found on stack");
return false;
}
}
/* state on top of the stack can shift under error, find the shift */
act = get_action(((Symbol)stack.peek()).parse_state, error_sym());
if (debug)
{
debug_message("# Recover state found (#" +
((Symbol)stack.peek()).parse_state + ")");
debug_message("# Shifting on error to state #" + (act-1));
}
/* build and shift a special error Symbol */
error_token = new Symbol(error_sym(), left_pos, right_pos);
error_token.parse_state = act-1;
error_token.used_by_parser = true;
stack.push(error_token);
tos++;
return true;
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
Lookahead Symbols used for attempting error recovery "parse aheads". /** Lookahead Symbols used for attempting error recovery "parse aheads". */
protected Symbol lookahead[];
Position in lookahead input buffer used for "parse ahead". /** Position in lookahead input buffer used for "parse ahead". */
protected int lookahead_pos;
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
Read from input to establish our buffer of "parse ahead" lookahead
Symbols.
/** Read from input to establish our buffer of "parse ahead" lookahead
* Symbols.
*/
protected void read_lookahead() throws java.lang.Exception
{
/* create the lookahead array */
lookahead = new Symbol[error_sync_size()];
/* fill in the array */
for (int i = 0; i < error_sync_size(); i++)
{
lookahead[i] = cur_token;
cur_token = scan();
}
/* start at the beginning */
lookahead_pos = 0;
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
Return the current lookahead in our error "parse ahead" buffer. /** Return the current lookahead in our error "parse ahead" buffer. */
protected Symbol cur_err_token() { return lookahead[lookahead_pos]; }
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
Advance to next "parse ahead" input Symbol. Return true if we have
input to advance to, false otherwise.
/** Advance to next "parse ahead" input Symbol. Return true if we have
* input to advance to, false otherwise.
*/
protected boolean advance_lookahead()
{
/* advance the input location */
lookahead_pos++;
/* return true if we didn't go off the end */
return lookahead_pos < error_sync_size();
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
Reset the parse ahead input to one Symbol past where we started error
recovery (this consumes one new Symbol from the real input).
/** Reset the parse ahead input to one Symbol past where we started error
* recovery (this consumes one new Symbol from the real input).
*/
protected void restart_lookahead() throws java.lang.Exception
{
/* move all the existing input over */
for (int i = 1; i < error_sync_size(); i++)
lookahead[i-1] = lookahead[i];
/* read a new Symbol into the last spot */
cur_token = scan();
lookahead[error_sync_size()-1] = cur_token;
/* reset our internal position marker */
lookahead_pos = 0;
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
Do a simulated parse forward (a "parse ahead") from the current
stack configuration using stored lookahead input and a virtual parse
stack. Return true if we make it all the way through the stored
lookahead input without error. This basically simulates the action of
parse() using only our saved "parse ahead" input, and not executing any
actions.
Params: - debug – should we produce debugging messages as we parse.
/** Do a simulated parse forward (a "parse ahead") from the current
* stack configuration using stored lookahead input and a virtual parse
* stack. Return true if we make it all the way through the stored
* lookahead input without error. This basically simulates the action of
* parse() using only our saved "parse ahead" input, and not executing any
* actions.
*
* @param debug should we produce debugging messages as we parse.
*/
protected boolean try_parse_ahead(boolean debug)
throws java.lang.Exception
{
int act;
short lhs, rhs_size;
/* create a virtual stack from the real parse stack */
virtual_parse_stack vstack = new virtual_parse_stack(stack);
/* parse until we fail or get past the lookahead input */
for (;;)
{
/* look up the action from the current state (on top of stack) */
act = get_action(vstack.top(), cur_err_token().sym);
/* if its an error, we fail */
if (act == 0) return false;
/* > 0 encodes a shift */
if (act > 0)
{
/* push the new state on the stack */
vstack.push(act-1);
if (debug) debug_message("# Parse-ahead shifts Symbol #" +
cur_err_token().sym + " into state #" + (act-1));
/* advance simulated input, if we run off the end, we are done */
if (!advance_lookahead()) return true;
}
/* < 0 encodes a reduce */
else
{
/* if this is a reduce with the start production we are done */
if ((-act)-1 == start_production())
{
if (debug) debug_message("# Parse-ahead accepts");
return true;
}
/* get the lhs Symbol and the rhs size */
lhs = production_tab[(-act)-1][0];
rhs_size = production_tab[(-act)-1][1];
/* pop handle off the stack */
for (int i = 0; i < rhs_size; i++)
vstack.pop();
if (debug)
debug_message("# Parse-ahead reduces: handle size = " +
rhs_size + " lhs = #" + lhs + " from state #" + vstack.top());
/* look up goto and push it onto the stack */
vstack.push(get_reduce(vstack.top(), lhs));
if (debug)
debug_message("# Goto state #" + vstack.top());
}
}
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
Parse forward using stored lookahead Symbols. In this case we have
already verified that parsing will make it through the stored lookahead
Symbols and we are now getting back to the point at which we can hand
control back to the normal parser. Consequently, this version of the
parser performs all actions and modifies the real parse configuration.
This returns once we have consumed all the stored input or we accept.
Params: - debug – should we produce debugging messages as we parse.
/** Parse forward using stored lookahead Symbols. In this case we have
* already verified that parsing will make it through the stored lookahead
* Symbols and we are now getting back to the point at which we can hand
* control back to the normal parser. Consequently, this version of the
* parser performs all actions and modifies the real parse configuration.
* This returns once we have consumed all the stored input or we accept.
*
* @param debug should we produce debugging messages as we parse.
*/
protected void parse_lookahead(boolean debug)
throws java.lang.Exception
{
/* the current action code */
int act;
/* the Symbol/stack element returned by a reduce */
Symbol lhs_sym = null;
/* information about production being reduced with */
short handle_size, lhs_sym_num;
/* restart the saved input at the beginning */
lookahead_pos = 0;
if (debug)
{
debug_message("# Reparsing saved input with actions");
debug_message("# Current Symbol is #" + cur_err_token().sym);
debug_message("# Current state is #" +
((Symbol)stack.peek()).parse_state);
}
/* continue until we accept or have read all lookahead input */
while(!_done_parsing)
{
/* current state is always on the top of the stack */
/* look up action out of the current state with the current input */
act =
get_action(((Symbol)stack.peek()).parse_state, cur_err_token().sym);
/* decode the action -- > 0 encodes shift */
if (act > 0)
{
/* shift to the encoded state by pushing it on the stack */
cur_err_token().parse_state = act-1;
cur_err_token().used_by_parser = true;
if (debug) debug_shift(cur_err_token());
stack.push(cur_err_token());
tos++;
/* advance to the next Symbol, if there is none, we are done */
if (!advance_lookahead())
{
if (debug) debug_message("# Completed reparse");
/* scan next Symbol so we can continue parse */
// BUGFIX by Chris Harris <ckharris@ucsd.edu>:
// correct a one-off error by commenting out
// this next line.
/*cur_token = scan();*/
/* go back to normal parser */
return;
}
if (debug)
debug_message("# Current Symbol is #" + cur_err_token().sym);
}
/* if its less than zero, then it encodes a reduce action */
else if (act < 0)
{
/* perform the action for the reduce */
lhs_sym = do_action((-act)-1, this, stack, tos);
/* look up information about the production */
lhs_sym_num = production_tab[(-act)-1][0];
handle_size = production_tab[(-act)-1][1];
if (debug) debug_reduce((-act)-1, lhs_sym_num, handle_size);
/* pop the handle off the stack */
for (int i = 0; i < handle_size; i++)
{
stack.pop();
tos--;
}
/* look up the state to go to from the one popped back to */
act = get_reduce(((Symbol)stack.peek()).parse_state, lhs_sym_num);
/* shift to that state */
lhs_sym.parse_state = act;
lhs_sym.used_by_parser = true;
stack.push(lhs_sym);
tos++;
if (debug) debug_message("# Goto state #" + act);
}
/* finally if the entry is zero, we have an error
(shouldn't happen here, but...)*/
else if (act == 0)
{
report_fatal_error("Syntax error", lhs_sym);
return;
}
}
}
/*-----------------------------------------------------------*/
Utility function: unpacks parse tables from strings /** Utility function: unpacks parse tables from strings */
protected static short[][] unpackFromStrings(String[] sa)
{
// Concatanate initialization strings.
StringBuffer sb = new StringBuffer(sa[0]);
for (int i=1; i<sa.length; i++)
sb.append(sa[i]);
int n=0; // location in initialization string
int size1 = (((int)sb.charAt(n))<<16) | ((int)sb.charAt(n+1)); n+=2;
short[][] result = new short[size1][];
for (int i=0; i<size1; i++) {
int size2 = (((int)sb.charAt(n))<<16) | ((int)sb.charAt(n+1)); n+=2;
result[i] = new short[size2];
for (int j=0; j<size2; j++)
result[i][j] = (short) (sb.charAt(n++)-2);
}
return result;
}
}